The objective of the research proposed in this renewal application remains the elucidation of the biochemical mechanisms by which hepatotoxic chemicals irreversibly injure liver cells. Studies over the last 2 years continue to support our hypothesis that activated oxygen species mediate the liver cell injury produced by such hepatotoxins as acetaminophen, bromobenzene and allyl alcohol. Additional studies provide new: insights into the mechanisms of irreversible injury by such activated oxygen species. Accordingly, the specific aims of the present proposal are: 1) to continue to explore the mechanisms whereby an acute oxidative stress lethally injures hepatocytes; 2) to further define the role played by an acute oxidative stress in the killing of hepatocytes by acetaminophen. bromobenzene and allyl alcohol; and 3) to assess the relevance of the conclusions derived from the use of cultured hepatocytes to the mechanism of liver necrosis in the intact animal. The first aim will entail study of the cellular source of the ferric iron necessary for the toxicity of activated oxygen species. The hypothesis to be tested is that the autophagocytosis of ferritin generates a pool of ferric iron required for the killing of cultured hepatocytes by an oxidative stress. In addition, studies are proposed on 1) the role of DNA damage and repair, 2) on the mechanism coupling GSH depletion to the initiation of lipid peroxidation, 3) on the role of microtubules in oxidative cell injury, and 4) on the role of mitochondrial damage as a mechanism of irreversible injury. The second aim will focus on the role of lipid peroxidation, changes in protein thiols, and mitochondrial alterations in the killing of cultured hepatocytes by acetaminophen, bromobenzene and allyl alcohol. In regard to acetaminophen, it is proposed to characterize 3 models (uninduced male hepatocytes, methylcholanthrene-induced and phenobarbital-induced hepatocytes) with respect to a) dose dependency, b) effect of inhibitors of metabolism, c) pattern of acetaminophen metabolism, d) potentiation by BCNU, e) the dependency of toxicity on a cellular source of ferric iron and f) the role of lipid peroxidation and the effect of antioxidants. These studies should indicate whether there are distinct mechanisms of irreversible cell injury under the differing conditions. In addition, new insight should be provided into the nature of these mechanisms. In pursuing the third aim attention will be given to liver iron metabolism as well as to the effect of antioxidants such as superoxide dismutase, catalase and other agents shown to be effective in vitro.